1. Field of the Invention
The present invention relates to an exhaust emission control system using a catalyst for 4-cycle engine in an outboard engine for a boat.
2. Description of the Prior Art
There is a conventionally known an exhaust emission control system in an outboard engine system, in which a catalytic converter is mounted in the exhaust system to purify the exhaust gas (for example, see Japanese Patent Application Laid-Open Nos. 3-23308 and 2-260893).
In general, a 2-cycle engine is mainly used as an engine for an outboard engine system for a boat because at is light in weight; it can be provided at a low cost, and it is easy to handle. However, a recent tendency is to replace the 2-cycle engine with a 4-cycle engine which is superior for countering exhaust emission, exhaust noise and the like.
However, the 4-cycle engine is large in bulk, as compared with the 2-cycle engine and in particular, includes an oil pan having a large volume. If a catalyst device is further mounted in an exhaust system of the 4-cycle engine, a problem is encountered in that the size of the outboard engine system itself, particularly, its upper portion, is further increased.